1. Field of the Invention
The present invention relates to a tandem AC generator composed of dual Lundell type rotors for vehicle (hereinafter, also referred to as “a tandem vehicle alternator” through the specification for short) having an improved brush structure and a method of producing a brush assembly of the tandem vehicle alternator.
2. Description of the Related Art
For example, there are various related-art techniques relating to a tandem vehicle alternator having a configuration in which a pair of Lundell-type rotors is placed in series (in a tandem connection) and each Lundell-type rotor generates and supplies an output voltage which is controlled independently. For example, Japanese patent laid open publications, No. JP-H5-83906 and No. JP-H5-137295 have disclosed such a tandem vehicle alternator. As has been well known, such a tandem vehicle alternator is equipped with a common-use slip ring and a pair of slip rings in order to supply electric power to exciting winding of the pair of the Lundell type rotors. The tandem vehicle alternator of the related art usually uses the common-use slip ring as commonly used and the pair of independent-use slip rings as used independently in order to reduce the size of the rotor along the axis direction or a longitudinal direction of a rotary shaft of the rotor, and through the slip rings the electric power is supplied to a pair of field windings in the pair of the rotors.
In such a configuration of the related art tandem vehicle alternator, because a current density is increased by an electric power supply mechanism which is commonly used by the pair of the rotors and which is composed of the common-use slip ring and a brush contacted to the common-use slip ring, the related art techniques have proposed a configuration in which the pair of the brushes is placed in a circumference direction of the slip ring. This mechanism will be also referred to as “the brush mechanism in which plural brushes are placed along a circumference direction of a slip ring”.
However, because such a brush mechanism of placing plural brushes along a circumference direction of a slip ring takes a complicated configuration of a brush assembly and requires complicated assembling work for assembling the brush assembly, and thereby needs a drastic change to brush assembling equipments. Those matters increase the manufacturing cost of a tandem vehicle alternator in addition to the reason of being a relatively low number of the tandem vehicle alternators to be produced. As a result, the tandem vehicle alternator of the related art has a drawback, namely, increases its manufacturing cost when compared with a general purpose vehicle alternator.